Aurora-B phosphorylation in vitro identifies a residue of Survivin that is essential for its localization and binding to INCENP in vivo

The chromosomal passengers aurora-B kinase, INCENP and survivin, are essential proteins that have been implicated in the regulation of metaphase chromosome alignment, spindle checkpoint function and cytokinesis. All three share a common pattern of localization and it was recently demonstrated that aurora-B, INCENP and survivin are present in a complex in Xenopus eggs and S.cerevisiae. The presence of aurora-B kinase in the complex, and its ability to bind the other components directly, suggests that INCENP and survivin could potentially be aurora-B substrates. This hypothesis was recently proven for INCENP in vitro. Here we report that human survivin is specifically phosphorylated in vitro by aurora-B kinase at threonine117 in its carboxyl alpha-helical coil. Mutation of threonine117 to alanine prevents survivin phosphorylation by aurora-B in vitro, but does not alter its localization in HeLa cells. By contrast, a phospho-mimic, in which threonine117 was mutated to glutamic acid, was unable to localize correctly at any stage in mitosis. These data suggest that phosphorylation of survivin at threonine117 by aurora-B may regulate targeting of survivin, and possibly the entire passenger complex, in mammals.